My CS-600 was purchased new in April so it seems safe to assume it has the lower power output. All of my gear is powered by (2) PS Audio Power Plant Premiers which removes the quality of the AC power from the wall as well as voltage issues from the table. The tubes have been rolled using NOS RCA and Sylvania black plates although the hum issues were present with the stock valves as well.
Mine exhibits a low level hum with the HD650, a headphone that I still listen to on occasion since even though there has been incredible breakthroughs in hp technology since their introduction, these cans with the right source and amp, can still make for enjoyable listening. Currently I am using the SS Bakoon AMP-R11 with them and they sound alive and exciting in comparison to the EAR HP4 using NOS RCA's.
I do not know about the CS-600, if there ever was a higher vs lower-power/sensitivity headphone output.
About the CS-300X(S) specifically, the Leben Managing Director himeself wrote me that there was two versions, and the they previously delivered the lower power version as standard, but could install the other version on demand. It is, as I stated, only two resistors that should be changed, any amp-mechanic could do that.
output, and the other has 800mW for high efficiency headphones.
Your CS-300X should be with 1000mW headphone output for low efficiency
headphones, therefore, the noise shall be improved by reducing the
headphone output power from 1000mW to 800mW..
At what impedace the 800/1000 mW is measured I do not know. Probably in the thirties (?)
Again - I have posted the diagram and the resistor values in question HERE
Edited by ardilla - 12/8/12 at 8:52am